Microstructure of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> hybrid electrospun nanofibers and their application in dye degradation

SiO₂/TiO₂ hybrid nanofibers were prepared by electrospinning and applied for photocatalytic degradation of methylene blue (MB). The phase structure, specific surface area, and surface morphologies of the SiO₂/TiO₂ hybrid nanofibers were characterized through thermogravimetry (TG), X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) analysis, scanning electron microscopy (SEM), etc. XRD measurements indicated that doping of silica into TiO₂ nanofibers can delay the phase transition from anatase to rutile and decrease the grain size. SEM and BET characterization proved that silica doping can remarkably enhance the porosity of the SiO₂/TiO₂ hybrid nanofibers. The MB adsorption capacity and photocatalytic activity of the SiO₂/TiO₂ hybrid nanofibers were distinguished experimentally. It was found that, although increased silica doping content could enhance the MB adsorption capacity, the intrinsic photocatalytic activity gradually dropped. The SiO₂ (10 %)/TiO₂ composite nanofibers exhibited the highest MB degradation rate, being superior to SiO₂ (20 %)/TiO₂ or pure TiO₂.     

Synthesis of spinel CuCo2O4 nanoparticles and its application in p-nitrophenol reduction

Journal of Sol-Gel Science and Technology - CuCo2O4 spinel nanoparticles were successfully preparedvia a sol–gel method, which were firstly employed in catalytic reduction of p-nitrophenol to...     

氨基酸等电点与氨基酸水溶液pH的区别

本文根据氨基酸在水中存在的型体及其摩尔分数,通过数学方法及合理的近似处理,说明氨基酸的等电点pI是氨基酸在水溶液中偶极离子型体的摩尔分数达到最大值时的pH,与其水溶液的浓度无关。氨基酸水溶液的pH不等于pI。     

公路桥梁钢筋混凝土构件的可靠度分析

本文参考有关统计资料,对我国新颁公路桥规JTJ023-85中钢筋混凝土构件承载能力的可靠指标进行了计算分析,并讨论了影响构件可靠度指标的几个主要因素。采用的方法是一种近似概率计算方法——一次二阶矩法,即只考虑随机变量的平均值和标准差两统计参数,对设计表达式进行线性化处理。结果表明,延性破坏构件在荷载组合G+Q_1下β平均值为3.6,在C+Q_2下β平均值为2.8;脆性破坏构件,则分别为4.1和3.3。这是新规范所反映的钢筋混凝土构件可靠度的基本水平。另外在某些荷载效应比值下提高了荷载安全系数和对脆性破坏构件考虑了工作条件系数,都较为合理。但构件在不同荷载情况下尚不能得到比较一致的可靠度。抗力和荷载效应的分项系数以及荷载的标准值还需进一步研讨。     

弹性分析法程序及箱形梁剪力滞系数的影响参数分析

本文首先介绍弹性分析的力法基础,流程框图及编制计算程序过程。通过程序来分析箱形梁剪力滞系数的影响参数,这里包括静定结构参数分析,其中探讨宽跨比、固端截面剪力滞系数的变化,宽高比的影响。截面型式对λ的影响,悬臂长度的影响以及荷载型式(集中力与均布力)对沿梁为直线变截面,抛物线变截面及等截面的悬臂固端梁的变化及影响。     

箱形桥梁估算剪力滞效应的两种简捷方法

讨论两种估算超静定箱梁剪力滞效应的简捷方法。第一种方法，在受荷的超静定体系中取一基本静定体系，将梁上的载荷、反力分别作用于基本体系上，然后利用叠加原理求得剪力滞系数．即利用λ＝∑λｉλｉ，这里．Ｍｉ，λｉ分别表示基本体系中的指定截面上求得的静定结构弯矩及剪力滞系数。第二种方法是在受荷的超静体系中，根据弯矩图中的反弯矩割切成若干简文体系。指定截面上的剪力滞效应（或剪力滞系数），即在所在的简支梁上求得．最后通过两等跨常截面承受均布荷载的连续证明两种简捷方法计算结果相当吻合．同样证实这两种简捷方法在工程上实用有重要意义。     

Preparation of ultrafine Cu1.5Mn1.5O4 spinel nanoparticles and its application in p-nitrophenol reduction

In this work, ultrafine Cu_1.5Mn_1.5O₄ spinel nanoparticles were successfully synthesized by a sol–gel method combined with two complexing agents, which was firstly employed in the reductive transformation from p-nitrophenol into p-aminophenol. The effect of calcination temperature on the crystal phase and microstructure of Cu_1.5Mn_1.5O₄ nanoparticles was investigated in this article. It was found that Cu_1.5Mn_1.5O₄ nanoparticles with pure spinel phase can be obtained at 500 °C with the help of EDTA acid–citric acid complexing agents. Below 500 °C, there exists some Mn₂O₃ impure phase. SEM characterization indicated that the particle size of the spinel Cu_1.5Mn_1.5O₄ rapidly increases above 600 °C. The catalytic experimental results show that the Cu_1.5Mn_1.5O₄ nanoparticles prepared at 500 °C exhibit the highest catalytic activity which is even superior to some precious metal catalysts. With the calcination temperature increasing, the catalytic activity of Cu_1.5Mn_1.5O₄ spinel nanoparticles gradually degrades which can be ascribed to the particle size growth of Cu_1.5Mn_1.5O₄. It can also be observed that all the oxide samples, namely CuO, Mn₂O₃ and Cu_1.5Mn_1.5O₄, possess certain catalytic ability for the transformation from p-nitrophenol into p-aminophenol. However, the catalytic activity of Cu_1.5Mn_1.5O₄ spinel nanoparticles is obviously higher than CuO and Mn₂O₃. Especially, Mn₂O₃ alone has very poor catalytic activity in the reduction of p-nitrophenol.

     

分子筛USY负载硼化钴非晶态合金催化剂的制备及其在催化硼氢化钠水解制氢中的应用

采用浸渍法与化学还原法相结合制备了一系列USY型分子筛负载非晶态合金硼化钴(CoB/USY)催化剂,并系统探究了该催化剂在催化硼氢化钠水解制氢中的催化活性。 XRD表征表明,USY分子筛载体上负载的活性组分CoB属于非晶态结构。 通过扫描电子显微镜,对比了负载型CoB/USY催化剂和粉末状CoB催化剂的微观形貌,发现非晶态合金活性组分CoB能够很好的分布在USY分子筛载体表面,较粉末状CoB有更高的分散度。 催化硼氢化钠水解制氢实验结果表明,相对于粉末状CoB催化剂,负载型CoB/USY催化剂在硼氢化钠水解制氢中具有更高的催化活性,30 ℃时NaBH₄水解产氢速率约为1.5 L/(min·g)。 反应动力学的计算结果显示,负载型CoB/USY催化剂在催化NaBH₄水解制氢反应中表观活化能约为65.9 kJ/mol,大大低于粉末状CoB催化剂的活化能(72.1 kJ/mol)。     

常截面悬臂箱梁跨间作用集中力和集中弯矩时负剪力滞效应的分析

本文按翼缘板纵向位移函数为4次抛物线变化规律研究跨间承受一集中力及集中弯矩时的负剪力滞效应。采用变分法求解,并探讨影响负剪力滞效应的有关因素,通过模型试验验证理论分析的正确性。